Turbine engine cooling system with an open loop circuit

ABSTRACT

A turbine engine system includes a heat source, a heat exchanger, a cooling medium inlet and a cooling medium outlet. The heat source includes a first passage. The heat exchanger includes a second passage and a third passage. The first and the second passages are configured in a closed loop circuit. The third passage is configured between the inlet and the outlet in an open loop circuit.

This patent application is a divisional of U.S. patent application Ser.No. 15/651,194 filed Jul. 17, 2017, which is a divisional of U.S. patentapplication Ser. No. 13/679,670 filed Nov. 16, 2012, which are herebyincorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION 1. Technical Field

This disclosure relates generally to a turbine engine and, moreparticularly, to a system for cooling a source within a turbine engine.

2. Background Information

A typical geared turbofan engine includes a gear train that connects afan rotor to a low speed shaft. The gear train may generate asignificant quantity of heat energy as a byproduct of turbine engineoperation, particularly as the gear train beings to wear. This heatenergy may be removed from the gear train and the engine utilizing acooling system. Such a cooling system may include a heat exchanger thatis configured in a closed loop circuit with a passage extending throughthe gear train. The heat exchanger may be arranged within the bypassduct of the engine.

To cool the gear train, at least a portion of the heat energy from thegear train is transferred into a cooling medium such as lubrication oilflowing through the passage. The heat exchanger subsequently transfersat least a portion of the heat energy from the cooling medium into airflowing through the bypass duct. However, at relatively low altitudesand/or in certain environments, the air within the bypass duct may berelatively warm. The effectiveness of the cooling system therefore maybe reduced when an aircraft is at such low altitudes for an extendedperiod of time; e.g., while waiting on a runway or in a holding patternin a relatively warm environment.

There is a need in the art for an improved cooling system for a turbineengine.

SUMMARY OF THE DISCLOSURE

According to an aspect of the invention, a turbine engine system isprovided that includes a turbine engine heat source, a heat exchanger, acooling medium inlet and a cooling medium outlet. The heat sourceincludes a first passage. The heat exchanger includes a second passageand a third passage. The first and the second passages are configured ina closed loop circuit. The third passage is configured between thecooling medium inlet and outlet in an open loop circuit.

According to another aspect of the invention, a turbine engine system isprovided that includes a gear train that connects a rotor to a shaft,and a plurality of heat exchange systems. A first of the heat exchangesystems transfers heat energy from the gear train to a second of theheat exchange systems. The first heat exchange system is configured in aclosed loop circuit, and the second heat exchange system is configuredin an open loop circuit.

The turbine engine system may include a case and a heat exchanger. Thecase houses the gear train, and includes a first passage. The heatexchanger includes a second passage and a third passage. The first heatexchange system includes the first and the second passages, and thesecond heat exchange system includes the third passage.

The turbine engine system may include a rotor and a shaft. The heatsource may include a gear train that connects the rotor to the shaft.The rotor may be a fan rotor or a compressor rotor. The shaft may be alow speed shaft.

The heat source may include a gear train. Alternatively or in addition,the heat source may include a bearing assembly, a seal assembly and/orany other device that generates heat energy as, for example, a byproductof turbine engine operation.

The turbine engine system may include a cooling medium reservoir that isfluidly coupled to the cooling medium inlet and configured in the openloop circuit.

The turbine engine system may include a flow regulator that is fluidlycoupled between the cooling medium inlet and the third passage.

The turbine engine system may include a flow regulator that is fluidlycoupled between the third passage and the cooling medium outlet.

The turbine engine system may include a flow regulator that is fluidlycoupled between the first and the second passages.

The turbine engine system may include a second heat exchanger with afourth passage. The first passage may be fluidly coupled between anoutlet of the second passage and an inlet of the fourth passage. Theheat source may include a fifth passage that is fluidly coupled betweenan outlet of the fourth passage and an inlet of the second passage. Thesecond heat exchanger may be or include a radiator.

The turbine engine system may include a second heat exchanger thatincludes a fourth passage. The fourth passage is configured with a fifthpassage in a second closed loop circuit. The fifth passage may beincluded in the heat source. The second heat exchanger may be or includea radiator.

The turbine engine system may include a second heat exchanger with afourth passage and a fifth passage. The fourth passage may be fluidlycoupled between an outlet of the second passage and an inlet of thefirst passage. The fifth passage may be fluidly coupled between anoutlet of the first passage and an inlet of the second passage.

The turbine engine system may include a cooling medium reservoir that isfluidly coupled between the fifth passage and the second passage and/orthe fourth passage.

The turbine engine system may include a flow regulator fluidly coupledbetween the cooling medium reservoir and the fourth passage. The flowregulator may be configured parallel with respect to the second passagewithin the closed loop circuit.

The cooling medium reservoir may be or include a fuel tank or an oil(e.g., lubrication oil) tank.

At least portions of the second and the third passages may be arrangedin a counter flow configuration.

At least portions of the second and the third passages may be arrangedin a cross flow configuration.

At least portions of the second and the third passages may be arrangedin a parallel flow configuration.

The turbine engine system may include a cooling medium reservoir that isconfigured in the open loop circuit. This cooling medium reservoir maybe or include a water tank.

The turbine engine system may include a cooling medium reservoir that isconfigured in the closed loop circuit. This cooling medium reservoir maybe or include a fuel tank or an oil (e.g., lubrication oil) tank.

The foregoing features and the operation of the invention will becomemore apparent in light of the following description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a cooling system for removing heatenergy from a turbine engine heat source;

FIG. 2 is a schematic illustration of a turbine engine system thatincludes an alternative embodiment cooling system for removing heatenergy from a turbine engine heat source;

FIG. 3 is a schematic illustration of a turbine engine system thatincludes another alternative embodiment cooling system for removing heatenergy from a turbine engine heat source;

FIG. 4 is a schematic illustration of a turbine engine system thatincludes still another alternative embodiment cooling system forremoving heat energy from a turbine engine heat source;

FIG. 5 is a schematic illustration of a counter flow heat exchanger;

FIG. 6 is a schematic illustration of a cross flow heat exchanger;

FIG. 7 is a schematic illustration of a parallel flow heat exchanger;

FIG. 8 is a perspective cutaway illustration of a heat exchange passagewith a plurality of ribs;

FIG. 9 is a perspective cutaway illustration of a heat exchange passagewith a plurality of pedestals;

FIG. 10 is a perspective cutaway illustration of a cross flow heatexchanger;

FIG. 11 is a perspective cutaway illustration of a core for the crossflow heat exchanger of FIG. 10;

FIG. 12 is a perspective cutaway illustration of an alternative coreembodiment for the cross flow heat exchanger of FIG. 10;

FIG. 13 is a partial sectional illustration of a turbine engine in whichthe heat source of FIGS. 1-4 may be included.

DETAILED DESCRIPTION OF THE INVENTION

A turbine engine includes various devices that generate heat energy as abyproduct of engine operation. These devices are referred to belowgenerally as “turbine engine heat sources”. Some examples of a turbineengine heat source include a gear train, a bearing assembly and a sealassembly. Several non-limiting examples of a cooling system for removingheat energy from at least one of the turbine engine heat sources aredescribed below.

FIG. 1 is a schematic illustration of a cooling system 10 for removingheat energy from a turbine engine heat source 12 such as a gear train.The cooling system 10 includes a passage 14 arranged within the heatsource 12, a heat exchanger 16, one or more flow regulators 18-20, acooling medium inlet 22, and a cooling medium outlet 24.

The passage 14 extends through the heat source 12 between a passageinlet 28 and a passage outlet 29. The passage 14, for example, mayextend through a case that houses one or more components of the heatsource 12. The passage 14 may be formed by one or more apertures,channels, gaps, chambers and/or other types of voids between components(e.g., gears, shafts, bearings, a case wall, etc.) of the heat source 12(e.g., gear train).

The heat exchanger 16 includes a plurality of heat exchange passages 30and 32. The first passage 30 extends through the heat exchanger 16between a passage inlet 33 and a passage outlet 34. The second passage32 extends through the heat exchanger 16 between a passage inlet 35 anda passage outlet 36. The heat exchanger 16 may be configured as adiscrete unit. Alternatively, the heat exchanger 16 may be included aspart of one or more other components of the turbine engine.

One or more of the flow regulators 18-20 are each adapted to controlwhether a cooling medium may flow within a respective portion of thecooling system 10. One or more of the flow regulators 18-20 may also oralternatively be adapted to control a flow rate at which the coolingmedium flows within the respective portion of the cooling system 10.Each of the flow regulators 18-20 may include or be configured as one ormore valves and/or a pump.

The cooling medium inlet 22 includes one or more discrete conduits(e.g., hoses). The cooling medium inlet 22 may also or alternativelyinclude one or more passages extending through or define by one or moreother components of the turbine engine.

The cooling medium outlet 24 includes one or more discrete conduits. Thecooling medium outlet 24 may also or alternatively include one or morepassages extending through or defined by one or more other components ofthe turbine engine.

The passages 14 and 30 and the flow regulator 18 are configured in aclosed loop circuit 38, and form a first heat exchange system 40. Thepassage outlet 34 is fluidly coupled to the passage inlet 28. The flowregulator 18 is fluidly coupled inline between the passage outlet 29 andthe passage inlet 33. The passage 32, the flow regulators 19 and 20, thecooling medium inlet 22 and the cooling medium outlet 24 are configuredin an open loop circuit 42, and form a second heat exchange system 44.The flow regulator 19 is fluidly coupled inline between the coolingmedium inlet 22 and the passage inlet 35. The flow regulator 20 isfluidly coupled inline between the passage outlet 36 and the coolingmedium outlet 24.

The heat source 12, as set forth above, may generate heat energy duringturbine engine operation. To remove this heat energy from the heatsource 12, the flow regulator 18 permits a first cooling medium tocirculate within the closed loop circuit 38. One or more of the flowregulators 19 and 20 also permit a second cooling medium to flow throughthe open loop circuit 42. The first cooling medium may be fuel,lubrication oil or refrigerant. The second cooling medium may be fuel,pure or treated water or refrigerant. The cooling medium inlet 22 mayreceive the second cooling medium from a cooling medium reservoir (e.g.,tank) or through a conduit that is fluidly coupled to a remote coolingmedium source such as a well or municipal water supply. The coolingmedium outlet 24 may exhaust the second cooling medium out of theturbine engine or into a gas path of the turbine engine.

The heat energy from the heat source 12 is transferred into the firstcooling medium flowing through the passage 14. The heat exchanger 16transfers the heat energy from the first cooling medium flowing throughthe passage 30 into the second cooling medium flowing through thepassage 32. This transfer of heat energy may vaporize some orsubstantially all of the second cooling medium, or the second coolingmedium may remain in a single (e.g., liquid) phase. The second coolingmedium as well as the heat energy carried thereby is subsequentlyexpelled from the cooling system 10 through the cooling medium outlet24.

FIG. 2 is a schematic illustration of a turbine engine system 46 thatincludes an alternate embodiment cooling system 48, the turbine engineheat source 12, and a cooling medium reservoir 50. In contrast thecooling system 10 of FIG. 1, the cooling system 48 also includes anotherpassage 52 arranged within the heat source 12, and a second heatexchanger 54. The cooling system 48 may also include various othercomponents (e.g., flow regulators, heat exchangers, etc.), which are notillustrated for ease of description.

The passage 52 extends through the heat source 12 between a passageinlet 57 and a passage outlet 58. The passage 52 may be formed by one ormore apertures, channels, gaps, chambers and/or other types of voidsbetween components (e.g., gears, shafts, bearings, a case wall, etc.) ofthe heat source 12 (e.g., gear train).

The second heat exchanger 54 is configured as a radiator (e.g., aliquid-to-air finned tube heat exchanger) with a heat exchange passage60. The passage 60 extends through the second heat exchanger 54 betweena passage inlet 61 and a passage outlet 62.

The passages 52 and 60 are configured in a second closed loop circuit64, and form a third heat exchange system 66. The passage outlet 58 isfluidly coupled to the passage inlet 61. That passage outlet 62 isfluidly coupled to the passage inlet 57. The cooling medium reservoir 50is fluidly coupled to the cooling medium inlet 22.

To remove heat energy from the heat source 12, the first and the secondheat exchange systems 40 and 44 may be operated as described above. Inaddition or alternatively, a third cooling medium may be circulatedwithin the second closed loop circuit 64. The third cooling medium maybe fuel, lubrication oil or refrigerant. The heat energy from the heatsource 12 is transferred into the third cooling medium flowing throughthe passage 52. The second heat exchanger 54 transfers the heat energyfrom the third cooling medium flowing through the passage 60 into airflowing through and/or around the second heat exchanger 54 (e.g.,radiator).

FIG. 3 is a schematic illustration of another turbine engine system 68that includes another alternate embodiment cooling system 70, theturbine engine heat source 12, and the cooling medium reservoir 50. Incontrast the cooling system 48 of FIG. 2, the passages 30, 52, 60 and 14and the flow regulator 18 of the cooling system 70 are configured in theclosed loop circuit 38, and form the first heat exchange system 40. Thepassage outlet 34 is fluidly coupled to the passage inlet 57. Thepassage outlet 58 is fluidly coupled to the passage inlet 61. Thepassage outlet 62 is fluidly coupled to the passage inlet 28. The flowregulator 18 is fluidly coupled inline between the passage outlet 29 andthe passage inlet 33. The passage outlet 29 may also be fluidly coupledto the passage inlet 57.

To remove heat energy from the heat source 12, the flow regulator 18permits the first cooling medium to circulate within the closed loopcircuit 38. The heat energy from the heat source 12 is transferred intothe first cooling medium flowing through the passages 14 and 52. Thesecond heat exchanger 54 transfers the heat energy from the firstcooling medium flowing through the passage 60 into air flowing throughand/or around the second heat exchanger 54 (e.g., radiator). The heatexchanger 16 may also be operated as described above to transferadditional heat energy from the first cooling medium into the secondcooling medium. Alternatively, the flow regulator 18 may substantiallyprevent the first cooling medium from flowing through the passage 30.

FIG. 4 is a schematic illustration of another turbine engine system 76that includes another alternate embodiment cooling system 78, theturbine engine heat source 12, the cooling medium reservoir 50, andanother cooling medium reservoir 80 (e.g., fuel or lubrication oiltank). In contrast to the cooling system 10 of FIG. 1, the coolingsystem 78 also includes a second heat exchanger 82.

The second heat exchanger 82 includes a plurality of heat exchangepassages 84-86. The first passage 84 extends through the second heatexchanger 82 between a passage inlet 87 and a passage outlet 88. Thesecond passage 85 extends through the second heat exchanger 82 between apassage inlet 89 and a passage outlet 90. The third passage 86 extendsthrough the second heat exchanger 82 between a passage inlet 91 and apassage outlet 92, and is configured as part of another heat exchangesystem such as a fuel/lubrication oil cooler. Various types andconfigurations of fuel/lubrication oil coolers are known in the art, andtherefore will not be discussed in further detail. The second heatexchanger 82 may be configured as a discrete unit. Alternatively, thesecond heat exchanger 82 may be included as part of one or more othercomponents of the turbine engine.

The passages 30, 84, 14 and 85, the cooling medium reservoir 80, and theflow regulator 18 are configured in the closed loop circuit 38, and formthe first heat exchange system 40. The passage 30 and the flow regulator18 are arrange in parallel, and fluidly coupled inline between an outlet93 of the cooling medium reservoir 80 and the passage inlet 87. Thepassage outlet 88 is fluidly coupled to the passage inlet 28. Thepassage outlet 29 is fluidly coupled to the passage inlet 89. Thepassage outlet 90 is fluidly coupled to an inlet 94 of the coolingmedium reservoir 80.

To remove heat energy from the heat source 12, the first cooling mediumcirculates within the closed loop circuit 38. The heat energy from theheat source 12 is transferred into the first cooling medium flowingthrough the passage 14. The second heat exchanger 82 transfers the heatenergy from the first cooling medium flowing through the passages 84 and85 into another cooling medium flowing through the passage 86 andcirculating within the cooler. In some modes of operation, the flowregulator 18 may cause the first cooling medium to bypass the heatexchanger 16. In other modes of operation, the flow regulator 18 maydirect at least a portion of the first cooling medium through passage 30in order to transfer additional heat energy from the first coolingmedium into the second cooling medium as described above.

One or more of the heat exchangers 16, 54 and 82 may have variousconfigurations other than those described above and illustrated in thedrawings. The heat exchange passages 30 and 32, for example, may bearranged in a counter flow configuration as illustrated in FIG. 5. Theheat exchange passages 30 and 32 may be arranged in a cross flowconfiguration as illustrated in FIG. 6. The heat exchange passages 30and 32 may be arranged in a parallel flow configuration as illustratedin FIG. 7. One or more of the heat exchange passages may each includeone or more heat transfer enhancement features such as ribs, pedestalsand/or any other types of protrusions and/or recesses that increasesurface area of the passage. For example, FIG. 8 illustrates a heatexchange passage 100 that includes a plurality of ribs 102. In anotherexample, FIG. 9 illustrates a heat exchange passage 104 that includes aplurality of pedestals 106. One or more of the heat exchange passagesmay each include a plurality of sub-passages. In the heat exchanger 108of FIGS. 10 and 11, for example, the second passage 30 includes aplurality of parallel and straight sub-passages 110. The third passage32 includes a plurality of parallel and straight sub-passages 112.Alternatively, as illustrated in FIG. 12, the third passage 32 mayinclude a plurality of parallel and tortuous sub-passages 114. Thepresent invention therefore is not limited to any particular heatexchanger and/or heat exchange passage types and/or configurations.

One or more of the heat exchangers 16, 54 and 82 may be manufacturedwith a metal powder bed process. The metal powder bed process mayutilize direct metal laser sintering (DMLS) and/or electron beam welding(EBM). The present invention, of course, is not limited to anyparticular heat exchanger manufacturing processes or techniques.

FIG. 13 is a partial sectional illustration of a geared turbine engine220 in which the heat source 12 may be included. The turbine engine 220is a two-spool turbofan that generally incorporates a fan section 222, acompressor section 224, a combustor section 226 and a turbine section228. Alternative engines might include an augmentor section (not shown)among other systems or features. The fan section 222 drives air along abypass flowpath while the compressor section 224 drives air along a coreflowpath for compression and communication into the combustor section226 then expansion through the turbine section 228. Although depicted asa turbofan gas turbine engine in the disclosed non-limiting embodiment,it should be understood that the concepts described herein are notlimited to use with turbofans as the teachings may be applied to othertypes of turbine engines such as a three-spool (plus fan) engine whereinan intermediate spool includes an intermediate pressure compressor (IPC)between the LPC and HPC and an intermediate pressure turbine (IPT)between the HPT and LPT.

The engine 220 generally includes a low spool 230 and a high spool 232mounted for rotation about an engine central longitudinal axis Arelative to an engine static structure 236 via several bearingassemblies 238. The low spool 230 generally includes an inner shaft 240(e.g., low speed shaft) that interconnects a fan 242, a low pressurecompressor 244 (“LPC”) and a low pressure turbine 246 (“LPT”). The innershaft 240 drives the fan 242 directly or through a geared architecture248 (e.g., gear train) to drive the fan 242 at a lower speed than thelow spool 230. An exemplary reduction transmission is an epicyclictransmission, namely a planetary or star gear system.

The high spool 232 includes an outer shaft 250 (e.g., high speed shaft)that interconnects a high pressure compressor 252 (“HPC”) and highpressure turbine 254 (“HPT”). A combustor 256 is arranged between thehigh pressure compressor 252 and the high pressure turbine 254. Theinner shaft 240 and the outer shaft 250 are concentric and rotate aboutthe engine central longitudinal axis A which is collinear with theirlongitudinal axes.

Core airflow is compressed by the low pressure compressor 244 then thehigh pressure compressor 252, mixed with the fuel and burned in thecombustor 256, then expanded over the high pressure turbine 254 and lowpressure turbine 246. The turbines 254, 246 rotationally drive therespective low spool 230 and high spool 232 in response to theexpansion.

The main engine shafts 240, 250 are supported at a plurality of pointsby bearing assemblies 238 within the static structure 236. It should beunderstood that various bearing assemblies 238 at various locations mayalternatively or additionally be provided.

In one non-limiting example, the gas turbine engine 220 is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 220bypass ratio is greater than about six (6:1). The geared architecture248 can include an epicyclic gear train, such as a planetary gear systemor other gear system. The example epicyclic gear train has a gearreduction ratio of greater than about 2.3:1, and in another example isgreater than about 2.5:1. The geared turbofan enables operation of thelow spool 230 at higher speeds which can increase the operationalefficiency of the low pressure compressor 244 and low pressure turbine246 and render increased pressure in a fewer number of stages.

A pressure ratio associated with the low pressure turbine 246 is thepressure measured prior to the inlet of the low pressure turbine 246 asrelated to the pressure at the outlet of the low pressure turbine 246prior to an exhaust nozzle of the gas turbine engine 220. In onenon-limiting embodiment, the bypass ratio of the gas turbine engine 220is greater than about ten (10:1), the fan diameter is significantlylarger than that of the low pressure compressor 244, and the lowpressure turbine 246 has a pressure ratio that is greater than about 5(5:1). It should be understood, however, that the above parameters areonly exemplary of one embodiment of a geared architecture engine andthat the present disclosure is applicable to other gas turbine enginesincluding direct drive turbofans.

In one embodiment, a significant amount of thrust is provided by thebypass flow path B due to the high bypass ratio. The fan section 222 ofthe gas turbine engine 220 is designed for a particular flightcondition—typically cruise at about 0.8 Mach and about 35,000 feet. Thisflight condition, with the gas turbine engine 220 at its best fuelconsumption, is also known as bucket cruise Thrust Specific FuelConsumption (TSFC). TSFC is an industry standard parameter of fuelconsumption per unit of thrust.

Fan Pressure Ratio is the pressure ratio across a blade of the fansection 222 without the use of a Fan Exit Guide Vane system. The low FanPressure Ratio according to one non-limiting embodiment of the examplegas turbine engine 220 is less than 1.45. Low Corrected Fan Tip Speed isthe actual fan tip speed divided by an industry standard temperaturecorrection of “T”/518.7^(0.5) in which “T” represents the ambienttemperature in degrees Rankine. The Low Corrected Fan Tip Speedaccording to one non-limiting embodiment of the example gas turbineengine 220 is less than about 1150 fps (351 m/s).

While various embodiments of the present invention have been disclosed,it will be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. For example, the present invention as described hereinincludes several aspects and embodiments that include particularfeatures. Although these features may be described individually, it iswithin the scope of the present invention that some or all of thesefeatures may be combined within any one of the aspects and remain withinthe scope of the invention. Accordingly, the present invention is not tobe restricted except in light of the attached claims and theirequivalents.

What is claimed is:
 1. A turbine engine system for a gas turbine engine,the system comprising: a turbine engine heat source including a firstpassage; a heat exchanger including a second passage and a thirdpassage; a cooling medium inlet; a cooling medium outlet; wherein thefirst and the second passages are configured in a closed loop circuit;and wherein the third passage is configured between the cooling mediuminlet and the cooling medium outlet in an open loop circuit; and asecond heat exchanger including a fourth passage that is configured witha fifth passage in a second closed loop circuit, wherein the fifthpassage is included in the heat source.
 2. The system of claim 1,wherein the open loop circuit is configured discrete from a fuel systemof the gas turbine engine.
 3. The system of claim 1, further comprisinga rotor and a shaft, wherein the heat source includes a gear train thatconnects the rotor to the shaft.
 4. The system of claim 1, furthercomprising a cooling medium reservoir that is fluidly coupled to thecooling medium inlet and configured in the open loop circuit.
 5. Thesystem of claim 4, wherein the cooling medium reservoir contains acooling medium that is supplied to the third passage through the coolingmedium inlet, and wherein the cooling medium comprises water.
 6. Thesystem of claim 1, further comprising a flow regulator that is fluidlycoupled between the cooling medium inlet and the third passage.
 7. Thesystem of claim 1, further comprising a flow regulator that is fluidlycoupled between the third passage and the cooling medium outlet.
 8. Thesystem of claim 1, wherein at least portions of the second and the thirdpassages are arranged in a counter flow configuration.
 9. The system ofclaim 1, wherein at least portions of the second and the third passagesare arranged in a cross flow configuration.
 10. The system of claim 1,wherein at least portions of the second and the third passages arearranged in a parallel flow configuration.
 11. The system of claim 1,further comprising a flow regulator that is fluidly coupled between thefirst and the second passages.
 12. The system of claim 1, furthercomprising a cooling medium reservoir that is configured in the openloop circuit, wherein the cooling medium reservoir contains a coolingmedium that is supplied to the third passage through the cooling mediuminlet, and the cooling medium comprises refrigerant.